The current mainstream of semiconductor devices including diodes, transistors, ICs, LSIs and VLSIs are of the resin encapsulation type. Epoxy resins have superior moldability, adhesion, electrical properties, mechanical properties, and moisture resistance to other thermosetting resins. It is thus a common practice to encapsulate semiconductor devices with epoxy resin compositions. In harmony with the recent market trend of electronic equipment toward smaller size, lighter weight and higher performance, efforts are devoted to the fabrication of semiconductor members of larger integration and the promotion of semiconductor mount technology. Under the circumstances, more stringent requirements including lead elimination from solder are imposed on epoxy resins as the semiconductor encapsulant.
Recently, ball grid array (BGA) and QFN packages characterized by a high density mount become the mainstream of IC and LSI packages. For these packages which are encapsulated only on one surface, the problem of warpage after molding becomes more serious. One approach taken in the prior art for improving warpage is to increase the crosslink density of resins to elevate their glass transition temperature. While lead-free solders require higher soldering temperature, such resins have a higher modulus at higher temperature and high moisture absorption. Thus there are left outstanding problems of delamination at the interface between the cured epoxy resin and the substrate and at the interface between the semiconductor chip and the resin paste after solder reflow. On the other hand, for resins with a lower crosslink density, more inorganic filler loadings are effective for providing low water absorption, a low coefficient of expansion and a low modulus at high temperature and expected to be effective for imparting reflow resistance as well. Regrettably, a concomitant increase of viscosity can compromise the flow during molding.
Japanese Patent No. 3,137,202 discloses an epoxy resin composition comprising an epoxy resin and a curing agent wherein the epoxy resin used is 1,1-bis(2,7-diglycidyloxy-1-naphthyl)alkane. This epoxy resin composition in the cured state has good heat resistance and excellent moisture resistance, and overcomes the drawback that cured products of ordinary high-temperature epoxy resin compositions are hard and brittle.
JP-A 2005-15689 describes an epoxy resin composition comprising (A) an epoxy resin comprising (a1) 1,1-bis(2,7-diglycidyloxy-1-naphthyl)alkane, (a2) 1-(2,7-diglycidyloxy-1-naphthyl)-1-(2-glycidyloxy-1-naphthyl)alkane, and (a3) 1,1-bis(2-glycidyloxy-1-naphthyl)alkane, and (B) a curing agent wherein 40 to 95 parts by weight of (a3) is included per 100 parts by weight of (a1), (a2) and (a3) combined. It is described that inclusion of 40 to 95 parts by weight of the resin of formula (1), shown later, wherein m=n=0 is preferred from the standpoints of flow and curability.